1. Field of the Invention
The present invention relates to a navigation system of a vehicle providing geographical position information to a driver during driving. More particularly, this invention relates to an improvement of an output signal processing unit of a fluxgate sensor used in the navigation system, which determines a moving direction of the vehicle.
2. Description of the Related Art
Generally, a conventional navigation system of a vehicle includes an output signal processing unit of a fluxgate sensor, which measures an angle of a moving direction relative to magnetic north in order to determine a geometrical position of a vehicle during driving. The output signal processing unit of a fluxgate sensor has a fluxgate sensor that obtains components of terrestrial magnetism both in the X and Y directions, where for example the moving direction is denoted as the X-axis and the direction perpendicular to it is denoted as the Y-axis, and measures momentarily the direction of the vehicle. The geometrical positions of the vehicle XX and YY are obtained from X and Y directions and velocity v of a velocity sensor of the vehicle, which are displayed on a map display, and thereby used in order to provided geographical position information of the vehicle to a driver.
Further, the above output signal processing unit of a fluxgate sensor includes a low pass filter removing a noise signal with a high frequency component due to variations etc. of the magnetic flux caused by a change of magnetic environment generated by driving the vehicle in the periphery of the flux. This low pass filter allows an output signal of the fluxgate sensor to be processed smoothly so that detecting accuracy of terrestrial magnetism is enhanced. Therefore, the above noise signal with a high frequency component does not cause the geographical positions to generate useless variations in the display and prevents the driver from making a mistake.
In the above output signal processing unit of a fluxgate sensor of the prior art, however, when the vehicle turns quickly, a high frequency component appears in the output of the fluxgate sensor, and the above low pass filter causes a time delay because it smoothly processes the high frequency component in the output of the fluxgate sensor. Consequently, a problem arises in that the detecting accuracy of direction in terrestrial magnetism declines, the following performance of the geometrical position becomes poor and the driver can easily make a mistake. Conversely the following performance becomes better when the low pass filter is not used, while the noise signal of the high frequency component can not be removed.